The present invention relates to a new and distinct cultivar of Hydrangea macrophylla and will be referred to hereafter by its cultivar name, ‘HORWACK’. ‘HORWACK’ represents a new big leaf hydrangea, a perennial shrub grown for landscape use.
‘HORWACK’ arose from an ongoing breeding program by the Inventor with objectives of developing new cultivars of Hydrangea with improved disease resistance, good branching, with induction of primarily sterile flowers.
‘HORWACK’ originated from a cross conducted in the Inventor's trial garden in April of 2004 in Dresden, Germany between the cultivar ‘Green Shadow’ as the female parent and an unnamed plant of Hydrangea macrophylla from the Inventor's breeding program, designated as clone no. 59-96/1. The new Hydrangea was selected as a unique single plant from the progeny of the above cross in April of 2006.
Asexual propagation of the new cultivar was first accomplished by softwood stem cuttings in Dresden, Germany in June of 2006 by the Inventor. Asexual propagation by softwood stem cuttings has determined that the characteristics of the new cultivar are stable and are reproduced true to type in successive generations.